300E: test sticks on 10% duty cycle - Page 3 - PeachParts Mercedes-Benz Forum

mhingram · #31 04-24-2003, 10:33 AM

I believe zhandax ordered it from here http://www.forparts.com/ Part was 3437224035

stevebfl · #32 04-24-2003, 11:26 AM

I went there and they recognized the part number. They also called it a housing and gave a price (about double my normal Bosch price). But it claimed the part status was a "non-stocked part". So, I am still curious.

pesuazo · #33 04-24-2003, 11:47 AM

Well, by zhandax posting it appears to be the a "Good" part.
If it is not stocked, they obviously get it from somewhere. At US 75.00 is still A LOT cheaper than US 500.00 for the whole housing.

Well, I did a search and found the post from M.B. DOC:

"Available only thru the aftermarket. BOSCH part number 3-437-224-035, very hard to calibrate.

MB part number 000-074-23-14 for the complete housing."

The bad news: I just realized, they were talking about a 1986 190E 16V 5 speed. We are talking about 1986 300E.
Would the potentiometers be the same?

The post title: "190e 16v problem ??? "

I guess we will have to wait until next weekend to look at the pics and find out the outcome.

Keep us informed

stevebfl · #34 04-24-2003, 12:45 PM

I wouldn't be surprised for this to fit all KE cars including v8s.

Chris Martens · #35 04-24-2003, 01:29 PM

Steve,

AFAIK the part with Bosch number 3-437-224-035 is the same for M103, M102 and the V8 with KE-Jetronic.

I still have no answer from my parts guy, it seems to be a non-stock part also in Germany ;-)

best regards,
Christian

1989 300TE

#36 04-24-2003, 02:19 PM

To speed things up, Ralph at Olympic had Bosch drop ship the part to me. The Bosch packing slip says "ship whse: Atlanta".
At least it is available within a weeks' time.

stevebfl · #37 04-24-2003, 05:09 PM

I've got one coming from my supplier. Won't be till next week cause I didn't want any special shipping. But I will find out about this.

Hurshi · #38 04-26-2003, 01:45 PM

I have found that when installing the potentiometer the point on the left side on the air meter housing where it mounts provides a fixed suppot on the left side and the only thing we need to adjust is the heights of the right side(see the picture).
By moving the right side of the potentiometer up or down you can move the slope (inputs and outputs curve) by some amount(picture on the next post).
The point here is to set the potentiometer so that it provides less resistance at idle and more resistance at rpms lower or higher than idle. To find this point I moved the pressure plate to the idle point and moved the potentiometer up and down till it gave its lowest reading and then tightened it.
The only thing that I don't understand is why is my potentiometer reading 4k resistance at 0 movement, 4.5k at idle and then goes back to about 1k at fully depressed position. This seems to be the opposite of what people are getting. I think its resistance should go from 1k at zero to about 4k when depressed.
I also don't know if my method above is correct. Can someone confirm this please.

Hurshi · #39 04-26-2003, 01:48 PM

The blue curve is not correct because it outputs the lowest resistance reading at the point above idle. The red curve is correct.
I should mention that the inside of the potentiometer looks different on my car. I don't know if it is the correct one for my car but this might be the reason it gives opposite readings(less resistance when fully depressed).

Hurshi · #40 04-26-2003, 01:52 PM

Here is how the potentiometer's contact points look in my car.

#41 04-28-2003, 03:27 AM

The resolution stinks because my magnifying glass is not large enough to capture both housings side-by-side. (guess I saved enough on this to get a real camera)

After checking the CD I see that the specs are in volts with the car running, so these passive resistance measurements are of dubious value, but here they are in ohms:

old new
pins 1-2 1.48 1.5
pins 2-3 5.66 5.41
pins 1-3 4.23 4.06

The dimension I was most concerned with was the height of the circuit board from the base of the housing. This would translate into how far the circuit board would protrude into the air meter, and affect contact of the wipers with the semiconductor pads.
These fears now seem unfounded. The old measures 20mm, the new 19.85mm.

Due to time constraints, I passed on replacing the intake gasket, but I did replace all the other rubber. I want a fresh start when I calibrate everything, and I would like to check for fuel leaks in broad daylight, but I did start the car and allow it to reach operating temp. Idle held fairly steady in the 600-800 rpm range. The real test will come next weekend.

pesuazo · #42 04-29-2003, 09:45 PM

Thanks for posting pictures.
It appears the days of buying the "whole air flow sensor" will be over. I have read many threads about similar problems, and the solution was always the big purchase.

Hurshi did a great job indicating a way to calibrate the pot with pictures. Here are some tests Hurshi, I hope they help.

The CD manual states: "Ignition OFF;Terminals 1-3 3.6 to 4.6 K Omhs. Terminals 2-3 slowly deflect airflow sensor by hand, resistance value continually rises up to 2/3 of deflectionn then drops off again" page 39 of "Testing Electrical Components of the KE Injection System" Doc 7.3-0121.
Another test:
Engine: Start
Voltage from Terminal 3 to ground 4.6 - 5.1 Volts
Engine: Idle
Voltage from Terminal 2 to ground 0.55 - 0.95 Volts
Page 35 of document above. These tests are for W124 models, I do not know if they apply to 190's as well.

zhandax, keep us posted, the pot is starting to look like a maintenance item now that we now where to get it.

stevebfl, your input is extremely valuable, you are the expert. Please let us know the outcome on the pot you ordered.

Thanks all for a great thread.

Duke2.6 · #43 04-29-2003, 10:36 PM

According to my "Model Year 1984" MBZ manual, which has a good overview and troublshooting section for the KE system the "airflow position indicator", which is, I believe, the same device referred to in this thread as "potentiometer" is part of the acceleration enrichment system, and I cannot find any other function that it supports. The device provides a rate of change signal.

Further, acceleration enrichment is CANCELLED at coolant temperatures of 80C and above, so the device serves no function that I can see once the engine is fully warmed up.

I bring this up because it doesn't appear to have any relationship to the original subject on duty cycle, and if the device is not functioning properly it should only affect acceleration response during warm-up.

Duke

#44 04-30-2003, 06:28 AM

The CD lists a 10% fixed duty cycle as indicative of a faulty airflow meter position sensor (the diagram points to the potentiometer), and the part was worn thru in the area of resting position (idle zone), just as stevebfl expected.
The 10% duty cycle is what first led me to this part.
A possible explanation is that the function(s) of this part evolved in the ensuing 4 years. (84-88)

Hopefully Steve will elaborate on the role of this housing when he has the opportunity to check out this part.
Personally, when I check and adjust the system this weekend, if the idle problem is gone, I am willing to ascribe success to replacement of this part. Just the 15 minutes of uneventful idle with no hunts to 1500 or 2000 RPM Sunday night has caused high expectations.

Even if this subassembly only contributes during warmup, it transmits a voltage to the ECU, and you would be amazed at the unintended consequences a stray/screwball voltage (or grounding of an intended voltage) can cause on an entire system.

stevebfl · #45 04-30-2003, 08:09 AM

After years of working on this system I find out new things every day.

A while ago I started recieving email from a gent who had a high idle problem. I replied with lots of what has been said here. I basically challenged him to identify his exact problem. He started calling me about this situation and I might have even been a little short with him one time. From the amount of time he was spending on this I thought he was a DIYer from this board. Well he solved his problem and he wrote me with extreme detail all his procedures.

It turns out that he is a tech from another board I participate in and the car was his wifes. I gave him my speel on how to ID where the air was coming from and I told him to start using various fixed substitute signals to find his problem.

He found that there is an exact voltage threshold from the POT that activates the idle control MAP. He found this voltage to be around .7v. Untill the voltage is that low the air valve is held at the ready state. This is a fixed state slightly more open than the average idle state.

I can tell you from many personal experiences that the manufacturers put only what they have to into service manuals. From every vantage they appear mortified by rampant access to info.

I think that this info is basically accurate and can state that from multiple fixes that the airflow meter pot is one of the most common idle problems. I have fixed two cars in the last couple months using his exact data. I too for a long time ignored the POT because of its stated function.